1. Field of the Invention
The present invention relates to a conductive member, and more particularly to a conductive member for use in electrostatographic processes for smoothing charges on, eliminating charges from, or establishing charges on an electrophotosensitive member, a transfer drum or transfer belt used in a transfer process, an intermediate transport belt, and a developing blade used in a developing process among others.
2. Description of the Related Art
Among chargers, there have been known corona chargers utilizing corona discharge and contact chargers. In a corona charger, since a high voltage of 4-8 kV must be applied to a wire, the wire and the case that surrounds the wire must be isolated from each other in order to prevent current leakage from the wire to the case. Thus, the corona charger has a drawback in that its size becomes larger. Also, since most discharge current flows to the case, a large magnitude of discharge is required in order to supply a required amount of current to an electrophotosensitive member. As a result, a large amount of ozone is generated, causing oxidation of apparatus components and deterioration of the surface of the electrophotosensitive member. Also, such ozone may be harmful to the human body.
In view of such drawbacks of corona chargers, contact chargers have been replacing corona chargers.
In contrast to the corona charger, the contact charger can charge, for example, an electrophotosensitive member at low voltage, thereby enabling implementation of a compact electrostatographic apparatus. The amount of generated ozone is {fraction (1/10)} to {fraction (1/100)} that in the case of the corona charger. The contact charger is implemented as a conductive brush, a single-layer roller, a multilayer roller, or a blade, among other forms.
In the case of a brush-type charger employing a conductive brush of, for example, rayon fibers that contain carbon, combings are unavoidable, causing current leakage to other chargers. Also, bristles of the brush fan out with use, potentially causing current leakage to a peripheral element. Charging tends to become nonuniform, causing minute ruggedness in electric potential on the surface of an electrophotosensitive member and resulting in formation of white or black lines on an image.
A single-layer conductive member, such as a roller, involves a problem in that applied voltage leaks to any scratch present on an electrophotosensitive member. Since the resistance of the conductive member depends sensitively on the amount of a conducting filler added to a base material, resistance control is difficult.
In the case of a multilayer conductive member, such as a roller covered with a tube, the structure is complex with a resultant increase in cost.
In the case of a conductive member such as a blade including a conductive base material and an insulating layer applied or bonded to the base material, when the insulating layer wears, the conductive base material may be exposed or may exfoliate. In the case of a blade including an insulative base material and a conductive layer applied to the insulative base material, the conductive layer may exfoliate. Also, cost increases as compared to the case of a single-body structure.
In view of the foregoing, an object of the present invention is to provide a conductive member for use in a contact charger capable of properly charging a subject member and that exhibits good durability and is easy to fabricate at low cost.
To achieve the above object, the present invention provides a conductive member which is used in a state in which the conductive member maintains contact with a subject member. The conductive member has a single-body structure and is formed of a polymeric base material that contains a conducting filler. The density of the conducting filler as measured at or in the vicinity of a portion of the conductive member that abuts the subject member is lower than that in the remaining portion of the conductive member, or substantially zero.
Preferably, the portion in which the density of the conducting filler is lower than that in the remaining portion or substantially zero ranges 20-120 xcexcm inwardly from an end of the conductive member at which the conductive member abuts the subject member.
Preferably, the true density of particles of the conducting filler or the specific gravity of particles including the conducting filler is greater than the specific gravity of the polymeric base material.
Preferably, the polymeric base material, which contains the conducting filler, is manufactured through centrifugal molding.
Preferably, the conductive member contains as the conducting filler at least carbon black.
Preferably, the conductive member contains as the conducting filler carbon black as a main filler, and one or more fillers selected from the group consisting of ionic conducting fillers and carbon black dispersants.
Preferably, the conductive member contains as the conducting filler carbon black in an amount of 0.1-5.0% by weight in relation to the amount of the polymeric base material. More preferably, the conductive member contains as the conducting filler one or more fillers selected from the group consisting of ionic conducting fillers and carbon black dispersants in an amount of 0.01-5.0% by weight in relation to the amount of the polymeric base material.
Preferably, the electric resistance of the conducting member is 1xc3x97105 to 1xc3x97109 xcexa9xc2x7cm.
Preferably, the polymeric base material is an elastomer.
Preferably, the polymeric base material is polyurethane or silicone rubber.
Preferably, the conductive member assumes a blade shape.
The conductive member according to the present invention has a single-body structure, and the portion that contains the conducting filler at relatively low density or contains no conducting filler ranges 20-120 xcexcm inwardly from an end of the conductive member at which the conductive member abuts a subject member (a member to be charged such as an electrophotosensitive member). Therefore, there can be prevented voltage leakage to any scratch present on the subject member, and coming off of the conducting filler from the portion of the conducting member that abuts the subject member. Also, by controlling the thickness of the low-distribution-density portion, the electric resistance of the conducting member can be controlled easily. Through employment of the single-body structure, the fabrication process becomes simple, and fabrication costs reduce. Also, exfoliation of a component element is not involved. Through employment of the polymeric base material; particularly, liquid polyurethane, the conductive member can be fabricated through centrifugal molding. Also, ooze of a plasticizer is not involved.
Through contact with the subject member, such as an electrophotosensitive member, the conductive member of the present invention can smooth out charges on, eliminate charges from, or establish charges on the subject member. Also, a function other than an electrical one can be imparted to the conductive member.